Objective: To evaluate the frequencies of various forms of inter-twin contact between monochorionic diamniotic (MD) and dichorionic diamniotic (DD) twins using four-dimensional (4D) sonography late in the first trimester of pregnancy.
Methods: Six MD and eight DD pregnancies were studied for 30 min with transabdominal 4D sonography at 10-11 and 12-13 weeks' gestation. The position of one fetus relative to the other was ascertained. The frequencies of 10 types of inter-twin contact were evaluated.
Results: There was no significant difference in the position of one fetus relative to the other at 11-13 weeks' gestation in MD and DD twins. There was a significant difference in the frequencies of head to arm contact between MD and DD twins at 12-13 weeks' gestation (p < 0.05). There were also significant differences in head to arm, head to trunk, arm to arm, and arm to trunk contact between 10 and 11 and 12 and 13 weeks' gestation in MD twins, respectively (p < 0.05).
Conclusions: The difference in the frequency of the type of inter-twin contact in MD and DD twins at 10-13 weeks' gestation may be due to early fetal neuromuscular development and differentiation of the neuromuscular system. However, the data and their interpretation should be viewed with some degree of caution because of the small number of subjects studied.